There are several ways to turn on the keychain light.
1. Press and hold down the button. The main white light turns on momentarily as long as the button is pressed down.
2. Quickly click the button twice. The main white light turns on steadily. You can tap the button again to change the brightness. Press and hold it down to turn the light off.
3. Quickly click the button three times. The auxiliary light turns on steadily. You can tap the button again to change to the 2nd auxiliary light. Press and hold it down to turn the light off.
The design is to prevent the light from accidentally turning on in the pocket. The 2 and 3 might take a few tries but it shall become easier once you are familiar to the clicks.